Epidemiology and ecology of Bacillus cereus biovar anthracis: A project to build capacities for the detection and investigation of novel pathogens

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Bacillus cereus biovar anthracis (Bcbva) combines the chromosomal background of B. cereus, an environmental bacterium, with the virulence plasmids of B. anthracis (Ba). These plasmids enable Bcbva to produce anthrax toxins and the anthrax capsule, causing lethal infection. While studies in animal models suggest that the virulence of Bcbva is comparable to that of Ba, morphological differences of Bcbva were detected. We showed that Bcbva is widespread in tropical Africa (from Cote d Ivoire (CI) to the Democratic Republic of Congo), with strains clustering in one unique genetic clade, displaying variability within the clade. In our main study area Taï National Park (TNP), CI, we demonstrated that Bcbva has caused major die-offs in wildlife since at least 1989. In TNP we found that every tenth carrion fly carries Bcbva. This suggests that these flies may play a role in Bcbva transmission, particularly for arboreal monkey species. An analysis of > 150 full Bcbva genomes from TNP points towards a continuous outbreak with several Bcbva lineages present in parallel and high Bcbva prevalence in areas with high mammal density. By developing a novel Bcbva specific assay we conducted seroprevalence studies in CI, revealing a wide distribution of Bcbva, mainly in areas where people live in contact to wildlife. We also identified other regions of CI where humans and livestock exhibit antibodies against Ba, caused by the Ba C branch, a lineage described in the United States. Research in the second funding period will focus on key questions regarding factors determining Bcbva distribution (1), Bcbva epidemiology (2) and the risk of emergence of so far unknown pathogenic bacilli (3). (1) Factors determining distribution will be investigated in field studies along an environmental gradient between two climatic regions in CI. These data will be complemented by in vitro studies examining growth and sporulation of Bcbva under varying environmental conditions. Combined results from both approaches will allow us to generate a risk map for Bcbva. (2) We will also investigate Bcbva epidemiology; specifically routes for infection in humans and animals, by comparing the epidemiology at two sites with known Bcbva occurrence and different environmental conditions. These data will be complemented with laboratory data, where we will test for Bcbva growth in different media (soil and fruits) and the interaction of Bcbva with possible vectors (carrion flies). To determine factors influencing human infection risk, we will analyze survey data collected from people with known exposition. (3) Lastly, we will perform experiments to examine the potential emergence of further atypical pathogenic bacilli by horizontal gene transfer of known virulence plasmids and the influence of new potential virulence factors. These three parts will allow us to determine risk factors for the emergence of Bcbva and other atypical pathogenic bacilli and to develop local countermeasures.